This invention relates to optical systems and in particular to a strip scanning optical system for scanning an object and progressively projecting a composite image of the same at an image surface, such as a xerographic or other photosensitive surface in a photocopying process.
There are three general types of strip scanning arrangements known to the prior art. In one, the optical system is fixed and the object and image surface move relative to the optics. In the second, the object is fixed and the optical system and image surface move at appropriate speeds relative to the object. In the third, the object is fixed and is scanned by a rotating mirror to relay an image of the object onto a moving image surface.
Typically, these prior art systems have in common the fact that they are capable of projecting a usable image only in one direction of scan motion. The return motion, whether it be return of the object, the optics, or the mirror, projects an image onto the moving image surface, but the image is moving in a direction opposite to that of the image surface and is therefore useless. Accordingly, the prior art has variously resorted to flyback arrangements to minimize "lost time" involved in the return motion of the scan mechanism. One system by which to accomplish scanning in both directions of object reciprocation is shown in U.S. Pat. No. 3,574,459 to Hartwig and Schnell, in which a single optical axis is rotated 180.degree. between successive scans by a prism.